Saw-tooth voltage generator utilizing integrator



J. G. LAWTON July 31, 1962 SAW-TOOTH VOLTAGE GENERATOR UTILIZINGINTEGRATOR 2 Sheets-Sheet 1 Filed Feb. 19, 1960 mmmm k AQY Re/ay fenine/e m r) INVENTOR. John G. Lawton Ji @ziw 9 a. a. Q bmvf 3,047,820Patented July 31, 1962 3,047,820 SAW-TOOTH VOLTAGE GENERATOR UTILIZINGINTEGRATOR John G. Lawton, Snyder, N.Y., assignor to the United Statesof America as represented by the Secretary of the Army Filed Feb. 19,1960, Ser. No. 10,003 Claims. (Cl. 331143) This invention relates tovoltage generators and in particular to an arrangement of componentswhereby a voltage as a function of time may be fed into an integratorand an integrated voltage output result.

It is a chief object of this invention to provide a sawtooth voltagegenerator such that the mean level of the output voltage will be subjectto adjustment.

It is a further object of this invention to obtain from an electronicsystem having a minimum number of electronic tubes an output voltagethat is an integral function of time, said output voltage being obtainedfrom an input voltage that is a function of time.

Other objects of the invention will become apparent as the descriptionthereof proceeds.

Accordingly, the instant invention will now be described with referenceto the accompanying drawings in which:

FIGURE 1 illustrates the wave form of the voltage output;

FIGURE 2 is a block diagram of the device;

FIGURE 3 is a circuit diagram of a practical system; and

FIGURE 4 illustrates the current voltage curve characteristics of backto back connected silicon junction diodes of the type used in theinvention.

Referring to FIGURE 1, it is seen that the average out-put voltage to bedeveloped is designated as Eav and that voltage increases in a linearmanner as a function of time until a value (Eav-I-Ae) is reached. Theslope of the wave form then becomes negative with the voltage decreasingin a linear manner as a function of time until a value Eav-Ae isreached. This cycle is then repeated. The average value of the voltageoutput Eav can be adjusted and means are herein disclosed for varyingthe average output voltage as desired.

The system used to generate the output waveform depicted in FIGURE 1 isillustrated in the block diagram of FIGURE 2. A reference voltage e isfed from a potentiometer P into a sensing element S. The sensing elementS comprises a 50,000 ohm resistor in series with back to back connectedsilicon junction diodes. The function of the 50,000 ohm resistor is toserve as a protective device when the equipment is first turned on. Thesensing element governs the operation of a relay Ry by energizing anarmature in the relay which has two stable positions. The two stablepositions of the relay provide for electrical connection to either oftwo input voltage terminals in the relay e+ and e. The voltage outputfrom the relay is consequently constant at one of two steady voltagelevels corresponding to the two positions of the relay, e-lor eas shownin FIGURE 2. The relay output is fed into the integrator I, and morespecifically to the grid of a pentode therein, as can be seen in thecircuit diagram, FIGURE 3.

The desired sawtooth voltage waveform is obtained at the output of theintegrator, designated I. The integrator is so designated that it ischaracterized by the transfer function: e =kfe,dt, wherein e, representsthe input voltage, e represents output voltage, and k represents theintegrator gain constant. It is readily apparent from the transferfunction that so long as the voltage input from the relay e remainsconstant, the output voltage e will vary linearly with time. The inputvoltage is kept continually at one constant value or the other constantvalue by the sensing element and relay, so that input to the integratore, is either 2+ or e, as designated in FIG- URE 2. Thus the output ofthe integrator I, being characterized by the aforesaid equation, isalways either linearly increasing or decreasing. The slope of the outputvoltage, either the positive or negative, is dependent on the integratorgain constant, k, and the magnitude of e+ or e-.

The input voltage to the integrator is kept constant by the side stablerelay, R, as seen in FIGURE 2. The operation of the side stable relay isas follows: Positive pulses of coil current move the armature to onecontact where it will remain until the advent of a negative pulse, whichwill return the armature to the other stable position.

The sensing element S monitors the difference between the output voltageof the integrator and the reference voltage e supplied by apotentiometer P. The sensing element exhibits two characteristic voltagethresholds. When either of these is exceeded, the sensing element causesthe relay to reverse so that the sign of the slope of the voltage outputof the integrator is reversed. The result is that the slope of theoutput voltage Waveform of the integrator will change and drive towardthe other threshold. Since one terminal of the sensing element S isconnected to the potentiometer slider at a voltage lever e it is clearthat the output voltage of the integrator is limited to the region e +eand e +e where e and e; are the upper and lower thresholds of thesensing element. See FIGURE 4. Further it is clear that any adjustmentof the potentiometer results in a change of the average value of theoutput waveform. If the characteristics of the sensing element aresymmetrical, i.e., if e =e =Ae, then the average voltage, e at theslider of the potentiometer will be equal to the average of the outputwaveform. FIGURE 4 illustrates the voltage current characteristics ofthe silicon junction diodes used in the sensing element.

FIGURE 3 is a circuit diagram illustrating a practical embodiment anduse of the system. The ideal integrator of the block diagram, FIGURE 2,has been approximated by the electronic circuit consisting of threevacuum tubes and associated components. The selection of components andtubes will determine the gain constant, k, of the integrator. \It isseen that because of the relative arrangernent of the relay and sensingelement no current can flow through the relay coils until the differencebetween the output voltage of the integrator, I, and the voltage e atthe slider of the potentiometer P reaches the reverse breakdown or Zenervoltage of the appropriate diode. Thereafter, any increase in voltageresults in an extremely rapid increase in current causing the relay R tobe switched to its other stable position and thus reverse the slope ofthe output voltage. As pointed out in the foregoing, if two diodes ofsimilar characteristics are chosen for use in the sensing element, thereference voltage 2, will equal the average output voltage e It is clearthat by moving the slider of the potentiometer, the average outputvoltage may be adjusted.

While various modifications of the disclosure may be resorted to andwill be apparent to those skilled in the art, and while the instantinvention has been described herein in a most practical embodiment, itwill be understood that the invention is not to be limited to thepreferred form described herein, except as limited by the scope ofappended claims.

What is claimed is:

1. A voltage generator having an adjustable mean level output voltagecomprising, in combination, a potentiometer having a slidable resistancearm, a coil electrically connected in series with said resistance arm; arelay having voltage input terminals and a reversible quickacting switchactuated by an armature; said armature being disposed so that it isunder the influence of currents in said coil; a sensing element inseries with said coil comprising back to back connected silicon diodes,said sensing element controlling the current in said coil and therebycontrolling the position of the switch in said relay; and an integratorin series with the output current of said relay and said sensing elementand having electrical components therein such that the voltage outputwill remain linear so long as the voltage input to the integrator is ata constant value.

2. A voltage generator as in claim 1 wherein the back to back connectedsilicon diodes have symmetrical characteristics.

3. A sawtooth voltage generator as in claim 1 wherein a large resistanceis in series in the conductor connecting said coil to said diodesthereby acting as a protective device when the equipment is first turnedon.

4. A voltage generator having an adjustable mean level output voltagecomprising, in combination, a potentiometer having an adjustableresistance means; a coil connected by a conductor in series with saidadjustable resistance means; a relay having two voltage input terminalsand a reversible quick-acting switch actuated by an armature; saidarmature being disposed to that it is under the influence of current insaid coil; a sensing element in series with said coil comprising back toback connected diodes having Zener voltage characteristics, said sensingelement monitoring differences in voltage between the voltage output ofthe potentiometer and a second voltage, said sensing element controllingthe current in said coil and thereby controlling the switch in saidrelay; and an integrator in series with the sensing element, a pentodein said integrator, and the output voltage of said relay biasing saidpentode in said integrator.

5. A sawtooth voltage generator as in claim 4 wherein said integratorhas electrical components therein such that the voltage output willremain linear so long as the voltage input to the integrator is at aconstant value.

References Cited in the file of this patent UNITED STATES PATENTS2,561,719 White Sept. 8, 1953 2,734,135 Wagner Feb. 7, 1956 2,887,592Stout et al. May 19, 1959 FOREIGN PATENTS 580,047 Canada July 21, 1959OTHER REFERENCES Keonig: Electrical Communication, vol. 36, November 2,1960, pages 132-138.

